From
Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
For more information, please contact the author.

AAPG
2003 Meeting, Salt Lake City, Utah, May 1114, 2003

Textural
Mapping with Lidar and Real- Time Kinematic GPS
on the Flow-unit Scale: An Example from the Pipe Creek
Early Albian Rudist Buildup, Central Texas

Jerome A. Bellian,
Charles Kerans, F. Jerry Lucia, and Ted Playton

Abstract:

A superb 3D exposure
of a rudist buildup and related facies fore-mound, back-mound, and beach
facies occurs along Pipe Creek as part of a Lower Albian Glen Rose carbonate
shelf. In situ and debris apron deposits that steadily grade northward
into patch reef toucasid communities and finally beach grainstones present
distinctly different rock fabrics and pore systems that resemble those
of producing rudist-dominated reservoirs in Mexico and the Middle East.
Due to the extremely rugose creek-bed exposure, with 5-meter mini-slot
canyons in places, discerning fine-scale caprinid build-ups from debris
aprons was extremely difficult. Without a 3D template or virtual base
map the three-dimensionality of the caprinid build-up would have been
difficult to impractical to capture. Existing maps and air photos of the
area were insufficient to convey quantitatively the localized complexity
of the Pipe Creek area and the nature of the creek-bed outcrop made conventional
photography unsuitable.

Ground-based lidar
(light detection and ranging) provided the 3D base template upon which
facies contacts between the in situ caprinid mounds and debris aprons
were mapped using a difference in weathering patterns between whole caprinid-test
casts with mud-rich matrix versus coarse inter-mound rubble with a high
percentage of touching-vug pore systems. These facies and their containing
high-order sequences were then mapped in the field "live" with
RTK GPS (real-time kinematic global positioning system). Textural mapping
was used to examine relatively smooth versus relatively jagged surface
micro-topography and correlated with the RTK GPS survey. Samples were
taken from each facies to be analysis and porosity and permeability modeling
in the ongoing effort to better constrain fluid flow in mixed-contact
vuggy limestone.